$ C = \left[\begin{array}{rrr}1 & 1 & 0 \\ 2 & 1 & 0 \\ 2 & 1 & 1\end{array}\right]$ What is $ C^{-1}$ ?
Solution: $ = \left[\begin{array}{rrr}-1 & 1 & 0 \\ 2 & -1 & 0 \\ 0 & -1 & 1\end{array}\right]$